Genetics homework help?

4. A true-breeding red snapdragon was crossed to a true-breeding white snapdragon. The F1 progeny were red. When F1*F1 matings were made, the following F2 progeny were observed:





1850 red


670 pink


831 white


Total: 3351





What are the appropriate parental, F1, and F2 genotypes in order to explain the above results?


(b) What phenotypic ratio would be expected from a testcross of an F1 snapdragon?


(c) Suppose the white phenotype is now lethal. What phenotypic ratio would be expected from a cross between F1 individuals?


Please help me understand this question. More important than the answer.

Genetics homework help?
http://en.wikipedia.org/wiki/Genetics
Reply:What you are dealing with here is imcomplete dominance. Instead of two alleles, one dominant and one recessive, as in regular Mendelian genetics, neither red nor white alleles dominate. However, I do not agree with what your teacher told you happened in the F1 generation. If you crossed purebred red (RR) with purebred white (WW), you should get 100% pink (RW). Then in the F2 generation, you should get a ratio of 1:2:1 (Red:Pink:White). That is not the ratio your teacher gave you. In b), the testcross of RW x WW should give you a 1:1 ratio (pink to white). In c), if the white phenotype is now lethal, you should get 1/3 red to 2/3 pink.





Maybe you should ask your teacher to clarify the question.

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